This invention relates, in general, to semiconductor devices, and more particularly, to a structure and a method of manufacturing a Laterally Diffused Metal-Oxide Semiconductor (LDMOS) device.
Semiconductor devices that are used in applications such as cellular base stations are required to operate at high frequencies. For these types of applications, Radio Frequency (RF) LDMOS power transistors are attractive because they provide good performance at frequencies in a range from 100 MHz to about 2 GHz.
RFLDMOS devices have been traditionally packaged in expensive metal/ceramic packages for thermal reasons. However, for certain low-to-medium power applications it is desirable to package these devices in plastic packages due to the lower cost of plastic encapsulation processes. In addition, plastic package technology has improved recently, and can now be used for packaging devices that are used in higher power applications.
The plastic mold compound comprising the plastic package causes certain parasitic capacitances within the device to increase and renders the device unacceptable for use in the GHz frequency ranges, where capacitance of the device becomes critical. The capacitances in the device are parasitics that can degrade RF performance metrics such as power gain and drain efficiency.
Accordingly, there is a need to provide an LDMOS device, particularly an RF LDMOS device that is designed for high frequency applications, that has low capacitance when packaged in a plastic package.